1. Field of the Invention
The present invention relates generally to a method and apparatus for receiving solar energy, and more particularly to a method and macro receiver for absorbing large amounts of radiant energy provided by heliostats, the method and apparatus particularly providing a large target area with low irradiation losses from the receiver.
2. Description of the Prior Art
Heliostats have been known since ancient times. Basically, heliostats constitute a plurality of reflective surfaces which track the sun and concentrate the reflected energy into a limited area. However, because of the finite image of the sun provided by the heliostats, and because of the errors both in tracking and in the optical surface of the heliostat, a relatively large receiver for the reflective solar energy is desirable. Since heliostats may be arrayed for many miles from the receiver, tremendous amounts of energy are focused upon the receiver thus generating high temperatures. As a result, and particularly since irradiation is a function of the fourth power of the absolute temperature of the receiver, a large receiver which accommodates the tracking and focusing errors of the heliostats and operates at high temperatures soon compromises the efficiency of the system as a result of irradiation losses from the receiver.
This is a long standing problem as illustrated by the Calver U.S. Pat. No. 294,117. More recently, Falbel U.S. Pat. No. 3,841,302; Cummings U.S. Pat. No. 3,869,199; and Levi-Setti U.S. Pat. No. 3,899,672 illustrate a continuing interest in the problem of concentrating solar energy.